Prestressed rolling mill and control



Nov. 3, 1970 A. KIGGELL E I 7 3,537,285

PRESTRESSED ROLLING MILL AND CONTROL- I Filed Dec. 20, 1965 I zsneets-sheet 1 TRANSDUCER L PREssuRE- vALv'E/ lNvE'NToRS ANNE Kmaeru.

Q BY Dcums S-russs' Mud, lbnw'-M\L A'r'roauau Nov. 3,1970 A. KIGGE LLETAL 3,537,285

PRESTRESSED ROLLING MILL AND CONTROL Filed Dec, 20, 1965 2 Sheets-Sheetz l )27 VALVE\ F/GZ.

INQENTQQRS ANNE Kmnsu. DEnms STUBBS BY MAMMM+-MI5 ATTORNE v UnitedStates Patent 3,537,285 PRESTRESSED ROLLING MILL AND CONTROL AnneKiggell, London, and Dennis Stubbs, Sheflield, England, assignors toDavy and United Engineering Compay Limited, Shelfield, Yorkshire,England Filed Dec. 20, 1065, Ser. No. 515,128 Claims priority,application Great Britain, Dec. 22, 1964, 52,116/ 64 Int. Cl. B21b37/08, 37/00 US. Cl. 72-8 12 Claims ABSTRACT OF THE DISCLOSURE Theinvention relates to a control scheme for a prestressed rolling mill, inorder that the mill shall roll constant gauge. A preload is applied tothe housing, but not to the rolls of the mill. The total s tress in thehousing due to both the preload and the rolling load is continuouslymeasured, as is the value of the preload. From the measurements, acontinuous indication is given of the variations in the roll gap due tovariations in the preload and rolling load and the preload is controlledby that indication to keep the gap constant.

This invention relates to rolling mills and is more particularlyconcerned with control systems aimed at maintaining constant gauge ofstrip and other elongate material issuing from a rolling mill.

Variations in the gauge of strip leaving a rolling mill emanate from theelastic nature of the components of the mill stand; the work between thework rolls of the stand produces a separating force which elasticallydeforms the chocks and housing of the stand. When the separating force,or rolling load, varies, due to changes in the incoming strip, thedeformation of the stand components and hence the roll gap between theworking surfaces of the rolls changes, with the result that the gauge ofthe outgoing strip is no longer constant. To mitigate the effects of thedeformation of the mill stand, it has been suggested to maintain thechocks under a preload greater than the rolling load; while prestressingin this way reduces the variations in gauge, it does not completelyeradicate them.

The present invention is directed to an automatic system forcompensating for variations in the deformation of stand components dueto variations in the rolling load, and broadly resides in preloadingthose parts of the mill, the deformation of which causes changes in theroll gap, under variations of the rolling load, with the exception ofthe rolls themselves, measuring the load to which those parts aresubjected, deriving therefrom a control signal representing variationsin the roll gap due to changes in the loads to which those parts and therolls are subjected during rolling, and controlling the preloadingautomatically by the control signal to maintain substantially constantthe roll gap, regardless of variations of the rolling load.

Another aspect of the present invention resides in the combination of arolling mill having two roll assemblies, between which the material tobe rolled is passed and preloading means for preloading those parts ofthe mill, the deformation of which causes changes in the roll gap undervariations of the rolling load, the preloading means applying no preloadto the rolls; and control system comprising means for continuouslymeasuring the total load to which said parts are subjected duringrolling, means for deriving therefrom a control signal representingvariations in the roll gap due to changes in the loads to which saidparts and the rolls are subjected during rolling and means forcontrolling the preloading means by the control signal to maintainsubstantially constant "ice the roll gap, regardless of variations ofthe rolling load.

In a preferred form of the invention, a rolling mill comprises a millframe, an upper and a lower roll assembly, each with a chock mounted inthe frame, means disposed between the chocks of the two assemblies forpreloading at least some of the chocks and the mill frame, means forgenerating a first signal representing the load to which the chocks andmill frame are subjected, means for generating a second signal dependenton the deformation of the rolls, and control means for controlling thepreloading means automatically to maintain the sum of the first andsecond signals constant.

The invention will be more readily understood by way of example from thefollowing description of a rolling mill and its control system,reference being made to the accompanying drawings, in which:

FIG. 1 schematically illustrates the mill and system, and

FIG. 2 shows a modification of the control system.

In FIG. 1, the mill stand has a pair of parallel housings, one of whichis shown at 12. Each housing has a window 13 in which an upper back-uproll chock 14 and a lower back-up roll chock 15 are slidably disposed.As usual, the necks of the back-up rolls 16 are journalled in chocks 14,15. The upper and lower chocks 17, 18 for the work rolls 20 are nestedin recesses in the backup roll chocks 14, 15 respectively. The lowerback-up roll chock 15 is supported on a pad 21 seated on the bottom ofthe window 13 while a screw 22, which can be driven by a screwdown motornot shown, engages the upper back-up roll chock 14 through a loadcell 23and a pad 24. In each housing there are a pair of hydraulic rams 25acting between the upper and lower back-up chocks 14, 15.

As well as acting as balance cylinders, the rams 25 are employed toapply a preload force to the chocks 14, 15 and to the housing 12, whilethe mill is rolling strip. For this purpose, the rams 25 of bothhousings are supplied from a source 26 of liquid under pressure througha pressure regulating valve 27 and the lines 28, and the valve 27 isautomatically controlled by an automatic control system. This controlsystem employs as the detector elements the loadcell 23, which measuresthe total force to which the chocks 14, 15 and the housing 12 aresubjected, and a pressure transducer 29, which is subjected to thepressure of the liquid in line 28 and which supplies an electricalsignal in accordance with that pressure. The :signal from loadcell 23 isapplied to an adding circuit 30 and also to a differencing circuit 31,to which the pressure signal from transducer 29 is also applied. Thedifference signal from circuit 31 is applied through a modifying circuit32 to the adding circuit 30. The output from circuit 30 is applied to acomparing circuit 33.

A reference signal on line 34 is obtained from a reference generator 35,which can be adjusted by hand and which is also adjusted automaticallyby the output on line 36 from an integrating circuit 37. Circuit 37 hasapplied to it the output from a direct acting thickness gauge 38, whichoutput is proportional to the difference between the detected gauge ofthe outgoing strip and the required gauge.

The screws 22 are coupled to a potentiometer or other transducer 40which gives a signal representing the mean position of the screws. Thissignal and the signal on line 34 are diflerenced in the subtractingcircuit 41, the difference signal being applied to the circuit 33 inwhich it is compared with the signal from adding circuit 30. Thedifference signal from circuit 33 is applied to the pressure regulatingvalve 27.

In operation, before rolling commences, a predetermined pressure isapplied to the rams 25; this pressure produces a preload which exceedspossible 'variations in rolling load. Thereafter, the screws 22 areadjusted to give a roll gap approximating that required for the desiredgauge. In each housing, therefore, the back-up roll chocks 14, 15 andthe frame 15 are subject to a preload P, which tends to lengthen thehousing 12 and compress the chocks 14, 15. None of the rolls 16, 20 aresubjected to this preload, where the work rolls 20 are not in contactprior to entry of the work.

When rolling commences, the preload is augmented by the rolling load W,so that the housing 12 and the chocks 14, 15 are now subject to forcesP+ W; however, the rolls 16, 20 are subject only to the rolling load W.

The roll gap S, i.e., the separation of the working surfaces of the workrolls 20 when the preload P and the rolling load W are zero, is set bythe screws 22 and measured by the potentiometer 40. The roll gapincreases when the hydraulic pressure is applied to the rams 25 to whereM; is the spring modulus of the housings and chocks and to S-|-(P+W)/M+W/M on the commencement of rolling, where M is a function of the rollparameters, permitting the calculation of an equivalent roll distortionwhich for illustrative purposes may be considered as a simple springmodulus. This expression represents the thickness of the material rolledand the control system operates to maintain constant the function(P+W)/M +W/M,-, regardless of variations in the rolling load W, and thusmaintains constant thickness of rolled material.

The loadcell 23 is subject to the sum of the preload and rolling load(P+W) and its electrical output is proportional to this sum. On theother hand, pressure transducer 29 has an output proportional to thepreload P so that the dilferencing circuit 31 gives an outputproportional to the rolling load W, only. The signal W from circuit 31is multiplied in the modifying circuit 32 by a corrective functionconsidered for illustrative purposes to be a. simple constant ofproportionality K. The modifying circuit 32, which may be apotentiometer or like device, may be adjusted to give varying values ofK, by hand or automatically or may be a non-linear function generator.

The sum output from adding circuit 30 is then the sum of the signalsfrom loadcell 23 and the modifying circuit 32, i.e.

(P+ W) +KW The modifying circuit 32 is set to give a value K equal to M/M so that the output from circuit 30 now represents the enlargement ofthe roll gap due to the preload and rolling load.

The generator 35 is set by hand to the required gauge (h'), so that thedifierencing circuit 41 applies the reference signal (h-S) to thecomparing circuit 33. The value for the enlargement of the roll gap ismaintained constant by comparing it with this reference signal in thecomparing circuit 33 and employing the error signal to control thepreload P, by means of the pressure regulating valve 27. Invthis way,the roll gap is kept constant, regardless of variations in rolling load,due to variations in the characteristics of the strip entering the milland as a result, the gauge of the outgoing strip is held substantiallyconstant. Furthermore, changes in gauge can be made by manual adjustmentof generator 35, while any adjustment of the screws 22 is automaticallyintroduced by the potentiometer 40.

As before mentioned, the thickness gauge 38 gives an output representingthe departure of the outgoing strip thickness from the required value(h') and this departure is indicated on a meter 42 and applied to theintegrating circuit 37. If the control circuit before described operatesentirely satisfactorily, the thickness gauge 38 will of course have zerooutput. If, however, there should be a 4 residual gauge error, therewill be a signal from the gauge 38, the time integral of which will beproduced on line 36 to modify the reference signal supplied by generator35 and thus cause the roll gap to be maintained constant at a value,differing from that previously held but more suitable for the requiredoutput gauge.

FIG. 2 illustrates a modification of the control system of FIG. 1, likeelements in both figures being given the same reference numerals. Theexpression for the roll gap and the rolled thickness:

where M is thespring modulus of the mill.

The gauge error is then In FIG. 2, the signal from pressure transducer29 is applied to modifying circuit 32 which introduces the factor l/M'Ihe modified signal is now applied to difierencing circuit 50, to whichis also applied the signal on line 51 from loadcells 23 via a modifyingcircuit 52 which introduces the factor l/M. The diflference signalproportion to (P+W)/M-P/M is fed to comparing circuit 33, to produce thegauge error signal which controls valve 27, as before. I

Although, in the mill illustrated and described, the preload is appliedbetween the two roll assemblies on opposite sides of the pass line, itwill be appreciated that the invention may be applied equally to otherforms of prestressed mill, such as that in which there are adjustablespacers between the two roll assemblies and thepreload is applied at thelocation of the pad 21 to force the roll assemblies towards one naother.In this case, the loadcell 23 is located in the spacers, so as to givean output signal representing the diiference between the preloadforceand the rolling load. In this case, the thickness of the rolledmaterial, which equals the roll gap modified by the compression of thespacers and the deformation of the rolls, is

where M, is the spring modulus of the spacers and M, is the springmodulus of the rolls, as before. (P-F) is given by the signal from theloadcells in the spacers and F is given by the output of thediflferencing circuit 31 (FIG. 1). The output of adding circuit 30 thusgives, as before, the deformation of the roll gap due to the preloadforce and the rolling load. Where the spacers are adjustable, as whenthey are screws, the initial roll gap value S may be introduced byconnecting the potentiometer 40 to those screws.

Where roll cambering equipment is supplied to provide controlled camberof the rolls for shape correction, the camber control equipment may beautomatically controlled by the signal from the difierencing circuit 31,since roll bending arises from, and is dependent on, the rolling load.Dependent on the manner in which the camber control is applied, this maydemand a complete revision of the control equations above, and hence thedetailed control equipment.

What is claimed is:

1. A method of automatically controlling a rolling mill to maintainsubstantially constant the thickness of rolled material comprisingpreloading parts of the mill, the deformation of which causes changes inthe roll gap under variations in the rolling load, said parts notincluding the rolls, continuously measuring the total load to whichthose parts are subjected due to the rolling load and the preload,continuously measuring the value of the preload, deriving a controlsignal representing variations in the roll gap due to changes in saidtotal load and said preload, and controlling the preloadingautomatically by said control signal to maintain substantially constantthe roll gap, regardless of variations of the rolling load.

2. A method according to claim 1 in which a first signal is obtainedrepresenting said total load to which said parts are subjected, a secondsignal is derived from said total load and said preload representing therolling load, and said first and second signals are combined together toobtain said control signal.

3. A method according to claim 1 in which a first signal is obtainedrepresenting said total load to which said parts are subjected, a secondsignal is obtained representing said preload, and first and secondsignals are combined together to obtain said control signal.

4. The combination of a rolling mill having two roll assemblies, betweenwhich the material to be rolled is passed and preloading means forpreloading those parts of the mill, the deformation of which causeschanges in the roll gap under variations of the rolling load, thepreloading means applying no preload to the rolls; and a control systemcomprising means for continuously measuring the total load to which saidparts are subjected during rolling, means for measuring the value ofsaid preload, means for deriving a control signal representingvariations in the roll gap due to changes in said preload and rollingload, and means for controlling the preloading means by the controlsignal to maintain substantially constant the roll gap, regardless ofvariations of the rolling load.

5. The combination according to claim 4 in which the measuring means arearranged to generate a first signal representing the total load to whichsaid parts are subjected, and in which there are means for generatingfrom said measuring means for said total load and said preload a secondsignal representing the rolling load, and means for combining thosesignals together to derive the control signal.

6. The combination according to claim 5 in which the means forgenerating the second signal comprises a detector for detecting thepreload and means for dilferencing the first signal and the preload.

7. The combination according to claim 4 in which the measuring means arearranged to generate a first signal representing the total load to whichsaid parts are subjected, and in which there are additionally a detectorfor generating a second signal representing the preload, and means forcombining the first and second signals together to derive the controlsignal.

8. The combination according to claim 7 in which the preloading meansare hydraulic rams between the roll assemblies, said detector beingarranged to detect the pressure of the hydraulic supply to the rams, andthe controlling means are pressure control means for the rams.

9. The combination according to claim 4 in which there are means forgenerating a reference signal, presenting the predetermined roll gapdeformation, means for differencing the first and second signals toobtain a difference signal, and means for comparing the differencesignal with the reference signal to obtain the control signal.

10. The combination according to claim 9 in which the reference signalis derived in part from means for indicating the undeformed roll gap.

11.-The combination according to claim 9 in which there is a directacting thickness gauge for measuring the thickness of the rolledmaterial leaving the mill and for giving a signal representing the gaugeerror, and means for applying the gauge error signal to the referencesignal generating means to change the reference signal until the gaugeerror is substantially zero.

12. In a rolling mill, having a plurality of rolls rotatively mountedabout substantially parallel axes, bearing means for supporting therolls, means supporting the bearing means for constraining theseparating forces imparted to the rolls by the product being rolled,means mounted on the supporting means and acting on at least one roll toset the separation between the rolls, adjustable actuator means actingon the supporting means directly through the bearing means to apply aforce which coacts With a separating force to oppose the forceconstrained by the supporting means, means to derive a control signalfrom the force constrained by the supporting means and the force appliedby the adjustable actuator means, and actuator varying means responsiveto the control signal to vary the force applied by the adjustableactuator means to maintain the work roll separation.

References Cited UNITED STATES PATENTS 2,903,926 9/ 1959 Reichl 72-83,159,063 12/1964 Fox 7221 3,247,697 4/ 1966 Cozzo 72240 3,285,04911/1966 Neumann 72246 3,327,508 6/ 1967 Brown 726 3,315,507 4/1967Marten 7216 FOREIGN PATENTS 955,164 4/ 1964 Great Britain.

MILTON S. M'EHR, Primary Examiner US. Cl. X.R. 72l6, 21

